1. Field of the Invention
This invention relates to automotive supercharger systems wherein a centrifugal supercharger is driven through a continuously variable transmission (“CVT”), and in particular to such a supercharger system having a speed multiplying gear assembly between the CVT and the supercharger wherein a housing of the gear assembly is selectively rotatably positionable relative to a housing of the CVT.
2. Description of the Related Art
Continuously variable transmissions, which are commonly referred to as CVTs, are used to improve fuel efficiency or horsepower utilization by allowing the drive shaft to maintain a constant angular velocity over a range of output velocities in the form of vehicle speed or angular velocity of a driven component such as a rotary compressor or supercharger. Alternatively, a CVT driven by a drive shaft of variable angular velocity may be used to precisely maintain or control the output angular velocity of the CVT output shaft. Compared with traditional gear-type transmissions having a distinct number of gear ratios, the unlimited number of gear ratios of a CVT allows the user to select a desired drive shaft angular velocity to control a desired output such as efficiency, power output, or speed. It has long been recognized in the automotive market that use of a CVT to drive a supercharger could provide significant performance enhancement. Although existing patents disclose use of a CVT with a supercharger, we are not aware of any commercial applications.
Conventional belt-driven CVTs typically comprise a variable diameter drive pulley with an input shaft, a variable diameter driven pulley with an output shaft, and an endless V-belt wrapped between the drive pulley and the driven pulley. Each pulley comprises a pair of opposing truncated cones or frustoconical sections defining an angular groove therebetween. Generally, one of the cones moves while the other remains fixed. Moving one cone in relation to the other varies the effective diameter of the pulley within which the CVT belt operates. Consequently, belt speed is a function of the effective diameter of the pulley which is, in turn, a function of the axial position of the cones relative to each other.
CVT belts typically have a profile similar to that of a conventional V-belt. In particular, they have a cross-section approximating an isosceles trapezoid; the upper edge being broader than the lower edge. The CVT belts are designed to fit between the opposing cones of the variable diameter pulleys as described above. Additionally, in order to avoid belt slippage while transferring torque from the drive pulley to the driven pulley, the cones of the driven pulley are biased axially inwardly to squeeze against the sidewalls of the CVT belt.
CVT belts have been designed to operate in wet or dry running conditions. Wet CVTs require or utilize liquid lubrication between the CVT belt and the pulley surface. As a result of this required lubrication, the orientation of wet CVTs is constrained by the need to properly distribute lubrication in the CVT housing. Dry running CVTs do not require a lubricant and therefore are not constrained to a certain orientation.
Because of their relative simplicity and favorable speed control characteristics, CVTs are ideal for driving an centrifugal supercharger in automotive applications. A problem, however, is that superchargers run at much higher rotational speeds than CVTs are capable of generating. A speed multiplying or overdrive gear unit is therefore needed between the driven pulley of the CVT and the supercharger.
Previous attempts have been made to drive an automotive supercharger through a CVT. For example, Teraoka et al., U.S. Pat. No. 5,361,744 discloses a supercharging device for an internal combustion engine which utilizes a CVT to control the speed of a supercharger impeller. The device includes a planetary gear set which acts to increase the rotational speed of the impeller over the output speed of the CVT.
Planetary gear sets are well known devices for reducing or multiplying rotational speed. These devices include a rotatably mounted sun gear, a plurality of rotatably mounted planet gears in toothed contact with the sun gear, and a ring gear surrounding and in toothed contact with the planet gears. In speed multiplying applications, the output of the planetary gear set is typically a shaft connected to the sun gear. The input of the planetary gear set may be made either through rotating the ring gear, or by rotating a planet gear carrier to which the planet gears are rotatably mounted.
A primary concern in installing automotive supercharger systems is the lack of available mounting space under the hood of a car. A supercharger system incorporating both a CVT and a gear assembly for increasing the output speed of the CVT is by necessity larger than conventional centrifugal supercharger systems and, therefore, needs to be as compact as possible and should be mountable in various orientations to make use of available space.
Since a dry-running CVT is mountable in various orientations, the only limitation on mounting orientation for such a supercharger system is the gear assembly, which needs to be internally lubricated. Internally lubricated gear assemblies typically have a required mounting orientation which is dictated by the locations of various features of the lubricating system, such as inlet ports, outlet ports, vents, drains, internal oil passages, etc.
What is needed is a compact CVT driven supercharger system having a gear assembly which is adjustably mounted or selectively moveable relative to the CVT such that the system can be adapted to make use of available under-hood space in a variety of vehicle applications.